In order to insure that the tap water or the water in a pool or spa is safe, it must be properly sanitized to prevent any health problems arising due to such contaminants as, for example, algae, bacteria, or any other pathogens which may be in the water. To this end, excess but determinate amount of biocidal chemical systems may be used to ensure that a biocidally effective amount of water-treating agents is present in the water body.
The more commonly used biocidal agents are chlorine or chloramines containing biocides. The chlorine can be in a number of different forms, e.g., sodium hypochlorite, chlorinated isocyanurates, etc. When any of these materials interact with water, they undergo hydrolysis to form free chlorine consisting of predominantly hypochlorous acid (HOCl), which is the sanitized agent, and hypochlorite ion.
The amount of chlorine remaining in the water is referred to as “residual chlorine”.
When chlorine dissolves in water, a mixture of hypochlorouse and hydrochloric acids is formed. Actually the hydrochloric acid always completely dissociates into hydrogen and chloride ions, whereas the hypochlorous acid only partially dissociates into hydrogen and hypochlorite ions. In either the hypochlorouse acid or hypochlorite ion form, chlorine is called “free chlorine residual”. Free residual chlorine has a highly effective killing power toward bacteria. As it is said before, chloramine is used as biocide too.
On the other hand, the residual chlorine or chloramine in water, especially drinkable water must be controlled, because if the dosage of free chlorine or chloramine in water exceeds the standard dosage, it would be toxic.
Accordingly, it would be desirable to provide an improved method and system for determining residual chlorine or chloramine in water to ensure that the amount of residual chlorine or chloramine in water is not harmful and there is enough amount of free chlorine or chloramine in water.
On the other hand, for measuring residual chlorine amount having relatively high concentration, an iodine titration method is used. In this method, a potassium iodide solution and the test solution sample containing residual chlorine are mixed, so that isolated iodine is titrated with sodium thiosulfate. After yellow color of the solution is thinned, a starch solution is added as an indicator. The mixed solution is titrated until blue color of starch is extinguished. By the amount of sodium thiosulfate required for titration, chlorine amount can be calculated by a certain equation. However, this method is also very complicated in terms of necessitating titration operation.
Iodometry is a general method in chemistry laboratories for measuring free chlorine in solutions by titration method. Obviously this method is not suitable for preparing free chlorine kits for routine use, because the titration methods need special care, several instruments and indicators and they are time consuming. In addition, starch is not a good indicator for the kit, because its complex with free iodine produces a turbid solution that determination of the intensity of the color for users of this kit would be difficult. There are several kits that use different suitable indicators to this end. For examples, benzidine compounds and DPD (N,N-diethyl-p-phenylenediamine) have been used for this purpose. Benzidine compounds are in group of carcinogenic, toxic, irritant materials and they are dangerous for environment. DPD is also toxic and corrosive. In addition, DPD test has an important limitation due to short time stability of induced dye after reaction of indicator and residual chlorine. According to this, recommended time for measurement of intensity of induced dye is only some seconds. Even if the concentration of residual chlorine would be more excessive of standard values, induced dye will be disappeared more rapidly.
Furthermore, various enzymes such as alpha-amylase, glucosaccharase, and glucose oxidase have been used as indicators for residual chlorine assay. However, enzymes are unstable for long time storages, because of decrease in enzyme activity.
Therefore, it would have been advantageous to overcome the above shortcomings.
The present invention discloses an inexpensive kit and suitable method for determination of residual chlorine or chloramine concentration in solutions by polyvinyl alcohol (PVA) as an indicator; which is odorless, colorless and nontoxic. Stability of induced color by this kit is more than 24 h.